1. Field of the Invention
The invention relates to a compact fiber coupler, and more particularly, to a polished fiber coupler without polishing substrates, and method of manufacturing the same.
2. Description of the Related Art
In optical communication systems, some or all of the signals/light beams transmitted in one optical fiber are usually coupled into another optical fiber. Furthermore, the signals/light beams with different frequencies were coupled or separated into another optical fiber. According to the disclosed literature and prior art, four kinds of optical devices have been successively commercialized. They are (1) planar light-wave circuit (referred to PLC) [M. K. Smit and C. V. Dam, xe2x80x9cPHASAR-Based WDM-Devices: Principles, Design and Applications,xe2x80x9d IEEE. Journal of Selected Topics in Quantum Electronics, vol. 2, pp. 236-250, June 1996.]; (2) micromachining optoelectronic system [M. C. Wu, xe2x80x9cMicromachining for optical and optoelectronic system,xe2x80x9d Proceedings of the IEEE., vol. 85, pp. 1833-1856, November 1997.]; (3) integration of the optical fiber and micro-optics [B. Lawrence and M. Shimazu, xe2x80x9cWaveguide Amplifiers Bring Integration Benefits,xe2x80x9d WDM Solutions, pp. 29-31, November 2000.]; and (4) all-fiber optics [referred to the web-site of Gould Fiber Optics company].
The functions, properties, prices and fabrication methods of the four kinds of optical devices mentioned above are obviously different from each other. The first and second optical devices have the disadvantage of high cost. The third optical device has the disadvantages of high production costs and yield bottleneck. The fourth optical device does not have the problems mentioned above.
The principal of the all-fiber is the theory of evanescent-coupling mechanism. As shown in FIG. 1, the evanescent field appears at the cladding portion 1, and the intensity of the evanescent field exponentially decays from the edge of the core 2. The power of the evanescent field, a decayed constant, is about the inverse of the wavelength. Therefore, at the cladding portion 1 near the edge of the core 2, the intensity of the evanescent field is very weak. In order to use the evanescent field in the optical fiber, the shape of the optical fiber needs to be changed. Then, two methods of fusion [refer to the web-site of Gould Fiber Optics company] and side-polished [M. Digonnet and H. J. Shaw, xe2x80x9cWavelength Multiplexing in Single-mode Fiber Couplers,xe2x80x9d Applied Optics, vol. 22, pp. 484-491, February 1983; and S. M. Tseng and C. L. Chen, xe2x80x9cSide-Polished Fibers,xe2x80x9d Applied Optics, vol. 31, pp. 3438-3447, June 1992.], which let the cores of the two optical fibers approach each other, are popularly introduced.
The process for fabricating a fused coupler consists of placing two or more optical fibers adjacent to each other, then fusing and stretching them to create a fusing-coupling region. Finally, as shown in FIG. 2, a protective component 3, such as a bear tube, packages the fusing-coupling region 4. In the fused coupler, the cross-section area and coupling length of the fusing-coupling region determine which output terminal output a signal/light beam. However, the fused coupler has a disadvantage of excessive structure variation. Further, light transmission almost disappears in the core. The fused coupler can""t achieve the requirements of high-speed transmission and low loss. Because the cross-section area of the optical fiber becomes thinner and thinner during the fusing step, the signal/light beam is hard to transmit through the fusing-coupling region.
The process for fabricating side-polished fiber [S. M. Tseng and C. L. Chen, xe2x80x9cSide-Polished Fibers,xe2x80x9d Applied Optics, vol. 31, pp. 3438-3447, June 1992.] consists of fixing an optical fiber in the groove of a polishing substrate, then creating the side-polished coupling region by polishing the cladding portion nearly to the edge of the core. Next, as shown in FIG. 3, a side-polished fiber coupler [M. Digonnet and H. J. Shaw, xe2x80x9cWavelength Multiplexing in Single-mode Fiber Couplers,xe2x80x9d Applied Optics, vol. 22, pp. 484-491, February 1983; and R.O.C. Patent No. 090825 by S. M. Tseng and S. P. Mar.] is formed by adjusting and adhering the side-polished coupling regions 5 of the side-polished fibers together.
In the side-polished fiber coupler, the cross-section area and coupling length of the side-polished coupling region determine which output terminal output a signal/light beam. However, the side-polished fiber coupler has a polishing substrate for fixing and polishing the optical fiber to cause large volume.
As shown in FIG. 4, Hussey and Minelly [C. D. Hussey and J. D. Minelly, xe2x80x9cOptical Fiber Polishing With a Motor-Driven Polishing Wheel,xe2x80x9d Electronics Letters, vol. 24, pp. 805-807, June 1988] provide another polishing method to reduce the volume and the time for polishing optical fiber. Next, Cryan and Hussey [C. V. Cryan and C. D. Hussey, xe2x80x9cFused Polished Single-Mode Fiber Couplers,xe2x80x9d Electronics Letter, vol. 28, pp. 204-205, January 1992.] provide another method for fabricating the fiber coupler by fusing two or more side-polished fibers. This fiber coupler has an advantage of small volume, but still has the disadvantage of polishing losses.
To solve the above problems, it is an object of the present invention to provide a compact fiber coupler that is applied to WDM and DWDM.
A feature of the invention is to provide a polishing substrate with a V-groove by utilizing standard microelectronic techniques and chemical etching. This process can adjust the radius curvature and depth of the V-groove, and the V-groove of the polishing substrate is used to fix and polish the optical fiber.
Another feature of the invention is to employ an optical fiber with a Bragg grating. Because of multiple reflection, the invention can obtain the advantage of low losses.
Another feature of the invention is to provide a polishing substrate with or without a lot of the same V-grooves by utilizing standard microelectronic techniques and chemical etching. A plurality of side-polished fibers are made up at the same time by polishing a plurality of optical fibers fixing therein.
Another feature of the invention is to obtain the side-polished fiber without polishing substrate by utilizing the organic solvent and corrosive liquid to remove it.
Another feature of the invention is to obtain the compact fiber coupler by fusing two or more side-polished fibers together.
The invention has an advantage of removing the mechanical stress remaining on the cladding by heating.
The invention has another advantage of obtaining a compact fiber coupler with small volume.